Heat exchanger having a mechanically assembled header

ABSTRACT

A heat exchanger and methods of manufacturing and assembling a heat exchanger, and more particularly to an air-flow heat exchanger having a mechanically assembled header for use in a motor vehicle. The heat exchanger comprises an all-metal bonded matrix including a plurality of substantially parallel metallic tubes and a plurality of metallic fins. The tubes have a heat transfer portion that is elongate in cross-sectional shape, and which comprises two opposing, longer sides, and two opposing shorter sides. At least one of the tubes is mechanically joined at a first end portion thereof to a first header of the heat exchanger by at least one compliant member. The compliant member extends around the first end portion of the tube to provide a seal and to permit relative movement between the mechanically joined tube and the first header due to thermal expansion and contraction of the matrix.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger and to methods ofmanufacturing and assembling a heat exchanger, and more particularly toan air-flow heat exchanger having a mechanically assembled header foruse in a motor vehicle.

BACKGROUND OF THE INVENTION

Typically, automotive vehicles are provided with an engine coolingsystem including a heat exchanger, which is usually referred to as aradiator. When the engine is running, heat is transferred from theengine to a coolant that flows through the engine. The coolant thenflows from the engine to the heat exchanger through a series ofconduits. At the heat exchanger, heat is transferred from the coolant tocooler air that flows over the outside of the heat exchanger. Thisprocess repeats itself in a continuous cycle thereby cooling the engine.

Heat exchangers are also used in air conditioning systems forintercoolers in turbochargers and superchargers, and for auxiliarycooling of electronic power supplies in electric vehicles.

A typical heat exchanger includes a series of tubes supported by twochambers, which are usually called headers, positioned at either end ofa heat exchanging portion, which is usually called the matrix. Thematrix comprises a series of parallel tubes which carry a liquid coolantbetween the headers, on the way from an input port and an outlet port tothe headers. Air flow between the tubes helps to dissipate heat in thecooling medium. To increase the surface area of the matrix and increasethe ability of the matrix to dissipate heat, the tubes are usuallyspanned by a series of fins that extend either in parallel in adirection transverse to the length of the tubes, or in a zigzagorientation between the tubes.

Although the headers may be partly or wholly of a polymer material, thematrix of the heat exchanger is of metal, for example an aluminiumalloy. The header has a base plate, also normally of metal, to which theends of the tubes are connected. Side walls of the headers may be ofmetal, but for reasons of cost are now often made from a plasticmaterial, which is secured to the metal base plate, for example bycrimps in the metal, with a seal between the metal base plate and headerside walls being made by a compliant, compressible gasket or o-ring thatextends around the periphery of the join between the base plate and sidewalls.

There are two known ways of fabricating such heat exchangers. One is touse “controlled atmosphere brazing” (CAB) to bond together the matrixand metal part of each header that is joined to the matrix. Any such CABprocess or welding process is referred to in this description as a“heating and fusing process”.

The other known way of fabricating such heat exchangers is to avoidwelding or brazing of adjacent metal components by using “mechanicalassembly” (MA) of the matrix and headers. In this description, the terms“mechanical joints” and “mechanically joined” are used to refer to anysuch non-welded or non-brazed joints in which adjacent components areheld together mechanically by separate in-contact components that arenot otherwise bonded together.

In the CAB process, flattened metal tubes are interspaced with metalfins that span the gaps between tubes, usually in a zigzag pattern. Inmany CAB heat exchangers, the tubes each comprise a single enclosedchannel or, alternatively, a pair of side-by-side single channels thatare separated by a longitudinally extending partition wall to form adouble enclosed channel. The tubes have a generally elongate,substantially rectangular cross-sectional shape, and comprise twoopposing, longer sides or faces that are substantially flat, and twoopposing curved shorter sides, or ends. The fins are then brazed to thelong sides and do not extend substantially beyond the bounds of theshort sides. The ends of each tube extend inside apertures in metallicheader base plates. The gap between adjacent metal components is kept toless than about 0.15 mm so that the gaps are spanned and sealed bysolder when the assembly is passed through a braze furnace to form thebraze joint between components. The metal components are preferably allof aluminium alloy to provide high thermal conductivity.

In the MA process, the fins, tubes and headers are all held together notby metallic joints but by friction or mechanical coupling. The fins,instead of being folded or corrugated to extend in the same direction asthe tubes, extend continuously at right angles to the tubes, andtherefore have apertures through which each tube passes. In thisarrangement, the fins are closely spaced apart in parallel, and usuallyextend to the opposite front and rear surfaces of the matrix. The tubeshave a circular cross-section and initially have a diameter less thanthe diameter of the fin apertures through which the tubes are inserted.The metal components are preferably all of aluminium alloy to providehigh thermal conductivity. A tool called a “bullet” is pressed down theinside length of each tube. The bullet has a diameter greater than theinitial inside diameter of the tubes, so that each tube is expanded topress against the apertures of the fins. This secures the fins to thetubes with a mechanical joint. The base plate of each header hasapertures for the ends of the tubes. The apertures have sufficientclearance for plastic or rubber sealing elements interposed between themetal of the tubes and base plates. A number of known ways are known tomake the seal tight, for example by using a conical tool pressed intothe tube ends to mechanically expand the tube ends and thereby compressthe seal.

Each process has certain advantages and disadvantages as compared withthe other. Heat exchangers made using the CAB process provide a higherheat exchange capacity for a given size heat exchanger and are in someways more mechanically robust because the tubes are flattened and extendto the front and rear faces of the heat exchanger, thereby protectingthe fins. A notable disadvantage is that the brazing process requires along passage through an expensive brazing furnace. Furthermore, duringoperation of an engine and radiator cooling system, the radiator tubesare subject to thermal cycling (rise and fall of the temperature of theheat exchanger components) which leads to stresses as neighbouring tubesmay expand to different degrees such that axial loads are imposed ontubes by their neighbours. Therefore, thermal expansion of the heatexchanger during use will not, in general, be even, and cracks candevelop in certain parts of the heat exchanger depending on the patternof the coolant flow, leading to leakage and premature failure of theheat exchanger. In particular, to maximise heat exchange capacity, thetubes are arranged side by side with the faces of neighbouring tubesopposing each other and defining a space or passage between the tubesfor the fins and through which a cooling medium such as air can flow.This geometry of the tubes is, therefore, favourable as it creates arelatively large surface area over which the cooling medium can passwhilst minimising the disruption to the air flow through the heatexchanger. However, these types of header/tube combinations are prone tofailure because of the stress concentrations that occur along theheader/tube joint, in particular around the nose of the tubes and wherethe tube walls are tightly curved.

The MA process avoids the need for a costly brazing furnace, and cantherefore be used to produce less expensive heat exchangers. Because thejoints between the tube ends and headers are mechanical, the compressionjoints can be designed to allow for some longitudinal movement betweenthe tubes and headers due to differing thermal expansion when the heatexchanger is heating up or cooling down. An all-mechanical heatexchanger therefore reduces or substantially eliminates thermal stressesbetween the heat exchanger components, thereby increasing heat exchangerreliability and lifetime. Such heat exchangers are, however, lessefficient at transferring heat for a given size, and thereforemechanically jointed heat exchangers have to be larger to provide thesame capacity. More space must therefore be provided for a larger heatexchanger in any given application. The fins, being parallel andextending to the front and back of the circular cooling fins, are alsomuch less robust than the zigzag fins nested between flattened tubes ofa heat exchanger formed using the CAB process. To maximise the heattransfer capacity, the fins are necessarily thin, about 0.1 mm inthickness, and such fins are easily deformed even by finger pressure.Any such damage will decrease flow of a cooling medium such as airthrough the heat exchanger. In a motor vehicle radiator, stones or gritcan sometimes hit the radiator, causing cumulative damage to the coolingpermeability of the matrix.

It is an object of the present invention to provide a heat exchanger andmethods of manufacturing and assembling a heat exchanger which addressesat least some of these issues.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a heatexchanger comprising: an all-metal bonded matrix including a pluralityof substantially parallel metallic tubes and a plurality of metallicfins, said tubes having a heat transfer portion, said heat transferportion being elongate in cross-sectional shape, and comprising twoopposing, longer sides, and two opposing shorter sides, and said finsbeing in between said opposing, longer sides of the heat transferportion of adjacent tubes; and a first header and a second header, eachof said tubes having at opposite ends of said tubes a first end portionand a second end portion, said first and second end portions beingjoined respectively to the first and second headers, the matrix therebybeing configured to transfer heat between an external medium and acoolant conveyed between said headers by said tubes; wherein at leastone of said tubes is mechanically joined at said first end portion tothe first header by at least one compliant member, said compliant memberextending around said first end portion to provide a seal with saidfirst end portion for coolant held within the heat exchanger andpermitting relative movement between said mechanically joined tube andthe first header owing to thermal expansion and contraction of saidmatrix.

The compliant member may be of a plastic or rubber material and ispreferably elastic such that is it resiliently deformable and thereforecapable or expanding and contracting according to an applied externalforce.

It should be noted that although this general description relatesspecifically to the first header and the first end portion of the tubesas having the mechanical joint, the second header and second end portionof the tubes may optionally have the same features of the first headerand first end portion of the tubes.

Alternatively, since the relative movement of the mechanically joinedfirst end portion of the tube and first header is accommodated for bythe compliant member between the first end portion of the tube and thefirst header, all of the tube second end portions may be joined to thesecond header by means of a bond between the metallic materials of thetube and the second header, made in a heating and fusing process.

Generally, the compliant member will be in direct contact with the tubeto provide a seal with the tube for coolant held within the heatexchanger and permitting relative movement along the length of the tubeof the mechanically joined first end portion of the tube relative to thefirst header owing to thermal expansion and contraction of the matrix.

The fins will, in general, extend between opposed longer sides ofadjacent tubes, the orientation of the tubes and fins being fixed in aheating and fusing process to form an all-metal bonded matrix. Thematrix will have opposite first and second faces, the longer sides ofthe tubes extending between the first face and the second face suchthat, in use, an external medium such as air flows through the matrixfrom the first matrix face to the second matrix face to effect thetransfer of heat. The heat transfer portion may therefore besubstantially rectangular in a cross-section extending between theopposite first and second faces of the matrix.

The relative movement permitted where there is a mechanical jointbetween the header and tubes prevents stress from building up owing touneven thermal expansion of the matrix and/or headers. The mechanicaljoint also permits a wide range of potential ways of joining the tubesto the headers, whilst still maintaining the benefits of an all-metalbonded matrix, in particular relatively high thermal heat transferefficiency within a compact form, and the potential for a robust designwhere fins are partially protected from physical damage between theadjacent elongate tubes.

The fins are metallically bonded or fused to the tubes, for example bythe application of heat in an oven in a CAB process, a solderingprocess, a brazing process or a calcination process. For convenience,all such heating processes in which a metal-to-metal bond is formed willbe referred to hereinafter as a “heating and fusing process”.

In a preferred embodiment of the invention, the longer sides of adjacenttubes are spaced substantially parallel with respect to each other andspaced apart in opposition to one another.

The connection of the tubes may be made to a part of the header nearestthe matrix. This part of the header may be a plate-like member, referredto herein as a base plate. To complete the header, this base plate maybe covered over with a cover that may be either permanently or removablyaffixed to the base plate, for example at a rim or lip that extends awayfrom a generally planar portion of the base plate. In a preferredembodiment of the invention, the first header has a first base plate andthe second header preferably has a second base plate. The, or each, baseplate then may have a plurality of apertures, each for making a flowconnection with a corresponding tube, which will have at least oneopening at both the first and second end portions.

When the end portions are received in the respective apertures, asealing portion of the compliant member is interposed between the firstbase plate and the mechanically joined first end portion around theaperture in order to mechanically join together the first end portionand the first header.

The compliant member then extends around the aperture to provide a sealwith the first base plate for coolant held within the heat exchanger.Generally, the compliant member will be in direct contact with the firstbase plate around the aperture to provide a seal around the aperture forcoolant held by the first header.

Each of the first end portions may be received within a correspondingone of the apertures of the first base plate The apertures may each havean elongate shape matching an elongate cross section of the tube, withclearance for receiving the tube and a sealing portion of the compliantmember

In a preferred embodiment of the invention, each of the second tube endportions is also mechanically joined to the second header by the secondbase plate at a corresponding aperture. Alternatively, any number of thesecond tube end portions may be joined to the second header with ametal-to-metal bond, in which case this is preferably formed in the sameheating and fusing process used to fuse the components of the matrixtogether. When there is a plurality of such tubes having all-metal bondsat both end portions, there may be at least one of the mechanicallyjoined tubes in between the all-metal bonded tubes.

Once joined the tubes may, in use, convey the coolant, which may, forexample, be a mixture of ethylene glycol and water, through the tube endopenings from one header to the other header, each tube having betweenthe tube end portions the heat transfer portion.

The fins preferably extend between opposed longer sides of adjacentpairs of tubes, the tubes and fins together forming the all-metal bondedmatrix. The matrix will, in general, have a first face and a secondface. It is a particular advantage of the invention if the longer sidesof each tube extend between the first and second faces of the matrix.This helps to provide mechanical rigidity to these opposite sides of thematrix. The longer sides of each tube are therefore preferablysubstantially flush with portions of the fins exposed at the oppositefaces of the matrix. Any contact with one of the faces can therefore besubstantially deflected or shielded by the sorter sides of each tube,which will, in general, be much more robust than fins, which aretypically relatively thin in comparison.

The arrangement of the matrix components is such that, in use, anexternal medium, for example air, flows through the matrix from thefirst face to the second face to effect the transfer of heat.

In preferred embodiments of the invention, the first end portion of themechanically joined tube has an expanded portion, the sealing portion ofthe compliant member being compressed around the aperture by theexpanded portion of the tube.

The compliant member is therefore compressed between opposing surfacesof each expanded first end portion and the corresponding aperture in thefirst base plate. The compressed compliant member therefore provides aseal between the, or each, mechanically joined first end portion and thecorresponding aperture in the first base plate in which the first endportions are received.

The opening of the first end portion therefore has internal dimensionsthat are outwardly expanded around the periphery of the opening.

The expanded end portion may be elongate in cross-sectional shape, andmay therefore comprise two opposing, longer sides, and two opposingshorter sides.

Each of the first tube end portions may have an expanded cross-sectionalshape relative to that of the heat transfer portion. This expansionreduces coolant flow resistance at the opening to each tube, while atthe same time acting to compress the sealing portion of the compliantmember between the first end portion and the base plate aperture. Thisfacilitates the formation of a good seal, particularly around corners oralong shorter edges of the tube end portion and compliant member.

There may be a tapering section of the tube that extends from the heattransfer portion and towards the expanded end portion, with an outwardlytapered shape, in which the distance between the two opposing, longersides of the tube is increased and the distance between the two opposingshorter sides is also increased. The compliant member is therebycompressed around the full extent of the aperture by the expandedportion of the tube.

The mechanically joined first end portion will, in general, have anopening for conveying the coolant. The two opposing, longer sides of theexpanded end portion may be splayed outwards proximate the opening andthe two opposing shorter sides of the expanded end portion may besplayed outwards proximate the opening. In this way, the first endportion is provided with the expanded end portion.

The expanded end portion may have a section with a substantiallyconstant cross-sectional shape in contact with the sealing portion ofthe compliant member. The benefit of having this constant shape over theexpected extent of longitudinal movement of the tube, is that thesealing portion is neither compressed nor expanded owing to the relativemovement of the mechanically joined first end portion and the firstheader owing to thermal expansion and contraction of the matrix. Thishelps to ensure a reliable contact, even when the tube moves in alongitudinal direction owing to thermal expansion or contraction.

Preferably, the degree of expansion and contraction in the, or each,mechanical joint accommodated for in the design of the heat exchanger,when used in an automotive environment, equates to a temperature rangeof −40° C. to 120° C.

The compliant member may have a base portion and at least one projectingportion. In preferred embodiments of the invention, the base portion isseated on a surface of the first base plate and the, or each, projectingportion extends through a corresponding one of the apertures in thefirst base plate. In this way, the sealing portion of the compliantmember is interposed between the first base plate and the mechanicallyjoined first end portion.

There may be a separate one of the compliant members for each of theexpanded tube end portions. In this case, each of the compliant membersmay extend through a corresponding aperture in the header or base plate,whereby each of the compliant members is interposed between acorresponding expanded tube end portion and the aperture.

Alternatively, the base portion of the compliant member may be a unitarycomponent, for example, a sheet with a plurality of apertures therein,each of the apertures in the sheet having a raised rim that provides theprojecting portion, and each of these rims extending through acorresponding aperture in the first base plate. In this way, each of therims is interposed between the first base plate and the mechanicallyjoined first end portion to provide the sealing portion.

The base portion of the compliant member is seated on an externalsurface of the first base plate facing substantially towards the matrix.Alternatively, the base portion of the compliant member may be seated onan internal surface of the first base plate facing substantially awayfrom the matrix.

When one or both of the headers has a base plate, this may have aperiphery and a cover which is joined to this periphery. The firstheader cover and the sheet may then extend to the periphery to provide aseal around the periphery between the base plate and cover.

The header and/or base plate need not be made from metal. The headerand/or base plate may be of polymer material. A polymer material headercover may be sealed to the corresponding polymer material base plate bya bonded seam, for example, glued or vibration-welded, to form a polymerbond.

Alternatively, the polymer cover of the header and the polymer materialof the first base plate may have between these components at least oneclip retaining feature by which the cover of the first header is securedto the first base plate.

The heat transfer portion may be substantially rectangular incross-section in a plane extending transversely to the length of thetubes.

Adjacent first end portions may have separate compliant members, howeverin preferred embodiments, adjacent tube ends have compliant members thatare provided by a unitary component.

There are two ways in which relative movement can be accommodated by thecompliant member. The compliant member may be capable of flexing inorder to permit the relative movement of the tube end portion.Alternatively, or additionally, the compliant member may be capable ofsliding in contact with the expanded tube end portion in order to permitthe relative movement of the tube end portion.

As long as one side of the matrix is mechanically joined to thecorresponding header, the other side of the tubes may still be fused toa metal header, as the relative movement of the compliant side willprevent stress build up at the fused side. Therefore, at least one ofthe tubes may have one end portion that is joined by means of anall-metal bond to the corresponding metallic header or metallic baseplate.

According to a second aspect of the invention, there is provided amethod of assembling a heat exchanger from a matrix, a first header anda second header, the matrix including a plurality of elongate andsubstantially parallel metallic tubes and a plurality of metallic fins,said tubes having a heat transfer portion, said heat transfer portionbeing elongate in cross-sectional shape, and comprising two opposing,longer sides, and two opposing shorter sides, and said fins being inbetween said opposing, longer sides of the heat transfer portion ofadjacent tubes and being joined by all-metal bonds to said adjacenttubes, each of said tubes having at opposite ends of said tubes a firstend portion and a second end portion, the method comprising the stepsof: joining said first and second end portions respectively to the firstand second headers such that the matrix is configured to transfer heatbetween an external medium and a coolant conveyed between said headersby said tubes, at least one of said tubes being mechanically joined atsaid first end portion to the first header by at least one compliantmember, said compliant member extending around said first end portion toprovide a seal with said first end portion for coolant held within theheat exchanger and permitting relative movement along the length of saidmechanically joined tube between said joined first end portion and thefirst header owing to thermal expansion and contraction of said matrix.

Also according to a third aspect of the invention, there is provided amethod of manufacturing a heat exchanger, the heat exchanger comprisingan all-metal bonded matrix, the method comprising the steps of: forminga first header, said first header having a first set of apertures;forming a second header, said second header having a second set ofapertures; forming a plurality of elongate metallic tubes, each of saidtubes having a first end portion and a second end portion and an openingat both of said end portions for conveying a coolant through the tubesfrom one header to the other header, and each tube having between saidend portions a heat transfer portion for transferring heat with anexternal medium, said heat transfer portion being elongate incross-sectional shape, and comprising two opposing, longer sides, andtwo opposing shorter sides; forming a plurality of metallic fins;orienting the tubes and fins such that the tubes are substantiallyparallel with one another and with fins extending between said opposedlonger sides of adjacent pairs of tubes; using a heating and fusingprocess to join together said oriented tubes and fins to form anall-metal bonded matrix, said matrix having a first face and a secondface such that, in use, an external medium may flow through said matrixfrom said first face to said second face to effect said transfer of heatbetween the coolant conveyed by the tubes and the external medium;aligning said first tube end portions with the first set of aperturesand aligning said second end portions with the second set of aperturesand joining each of said end portions to the corresponding aligned setof apertures; and with at least one of said tubes, receiving said firstend portion within a corresponding aperture of said first set ofapertures and using a compliant member to join said tube to the firstheader in a mechanical joint between said first end portion of saidfirst header and the corresponding aperture within which said first endportion is received, the compliant member providing a seal around saidfirst end portion for said coolant and permitting relative movementalong the length of said mechanically joined tube between said joinedfirst end portion and the first header owing to thermal expansion andcontraction of said matrix.

The longer sides of the tubes preferably extend between the first faceand the second face of the matrix.

Optionally, at least one of the tubes may be joined at both end portionsto the corresponding headers by means of an all-metal bond in a heatingand fusing process between the end portions and the headers. There maybe a plurality of such tubes joined at both end portions to thecorresponding headers by means of an all-metal bond in a heating andfusing process, in which case it is preferred if there is at least oneof the mechanically joined tubes in between the all-metal bonded tubes.

Alternatively or additionally, the matrix may comprise at least onestrip that is substantially parallel with the tubes, the strip beingjoined to both headers by means of an all-metal bond between the stripand the headers. In preferred embodiments of the invention, the strip isa protective strip between which the tubes are sandwiched.

The method may comprise the steps of: forming a first base plate, thefirst set of apertures being provided in the first base plate; forming asecond base plate, the second set of apertures being provided in thesecond base plate; forming a first header cover and assembling the firstheader cover to the first base plate to form the first header; andforming a second header cover and assembling the second header cover tothe second base plate to form the second header.

When the second base plate is metallic, the method may comprise the stepof joining each of the tubes at the second end portions to the secondheader by means of an all-metal bond in a heating and fusing processbetween the second end portions and the second header.

The mechanically joined tube will, in general, have an outer wall. Themethod may therefore comprise the steps of outwardly expanding the wallin the first end portion relative to the wall in the heat transferportion. In this way, the sealing portion of the compliant member iscompressed in contact with the expanded wall in the end portion toprovide the seal and permit the relative movement of the tube endportion relative to the joined base plate owing to thermal expansion andcontraction of the matrix.

Prior to the expansion of the wall of the end portion, the method maycomprise the steps of inserting the first end portion into acorresponding one of the apertures with which the first end portion isaligned, and interposing the compliant member between this inserted endportion and the first header, and then expanding the corresponding endportion such that the first end portion compresses the compliant memberin order to form the seal around the expanded first end portion.

In a preferred embodiment of the invention, the first header has a wallthat extends around each of the apertures within which the first endportion is received, and the method comprises the step of expanding thiswall of the header inwards towards the received first end portionwhereby the sealing portion of the compliant member is compressed incontact with this expanded wall of the first header around the aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, andwith reference to the accompanying drawings, in which:

FIG. 1 is a schematic plan view of an assembled array of metallic tubesand metallic fins for a matrix for use in a heat exchanger according topreferred embodiments of the invention, prior to brazing of thecomponents;

FIG. 2 is a schematic view of the components of FIG. 1 when heldtogether by a temporary frame;

FIG. 3 is a perspective schematic view of a controlled atmospherebrazing (CAB) process used to braze together the components of thematrix of FIG. 1;

FIG. 4 is a cross-section view of the brazed matrix with an enlargedpartial view indicating how a metallic header base plate with internallyfitted compliant member is mechanically connected to end portions of thematrix tubes in a first preferred embodiment of the invention;

FIG. 5 is a cross-sectional view of a part of the matrix and header baseplate after connection to the ends of the matrix tubes, showing how thecompliant member has apertures that receive tube end portions so thatthe compliant member is interposed between the header base plate and endportions of the tubes;

FIG. 6 is a plan view along the direction VI-VI of FIG. 5, showing theinside of the header base plate, the compliant member and the tube ends;

FIG. 7 shows the connected header base plate and matrix of FIG. 5, andhow an expansion tool is moved in a longitudinal direction towards thetube ends;

FIG. 8 shows how the expansion tool has a number of bullet nosedprojections that are pressed into the openings of each of the tube endportions in order to deform each of the tube walls outwardly around thefull perimeter of each opening, and how the compliant members arethereby compressed in the process to make a seal with the tube endportions;

FIGS. 9 and 10 show how, after removal of the expansion tool, a headercover is connected to the header base plate to complete the assembly ofthe heat exchanger in the first preferred embodiment of the invention,following which coolant can be made to flow through the heat exchanger;

FIG. 11 is a cross-sectional view of a part of a metallic header baseplate and a compliant member which is to be fitted to an externalsurface of the header plate, for use in a heat exchanger according to asecond preferred embodiment of the invention;

FIG. 12 shows the header base plate and a compliant member of FIG. 11when fitted together;

FIG. 13 is a plan view of the external surface of the header base plate,taken along line XIII-XIII of FIG. 12;

FIG. 14 shows how, after tube end portions of the brazed matrix havebeen inserted through apertures in the compliant member, an expansiontool with a number of bullet nosed projections is pressed into theopenings of each of the tube end portions and also into cup-shapedportions of the metallic header base plate either side of each tube end;

FIG. 15 is a plan view of the inside of the header base plate showinginternal parts of the compliant member fitted to the header base plate,taken along line XV-XV of FIG. 14;

FIGS. 16 and 17 follow on from FIG. 14 and show in cross-section how thetool is used to deform outwardly the openings of each of the tube endportions, while at the same time deforming outwardly the cup-shapedportions of the metallic header base plate on either side of each tubeend portion;

FIG. 18 is a cross-sectional view of a part of a plastic material headerbase plate and a compliant member which is to be fitted to an internalsurface of the header base plate, for use in a heat exchanger accordingto a third preferred embodiment of the invention; and

FIG. 19 shows the header base plate and a compliant member of FIG. 12when fitted together;

FIG. 20 is a cross-sectional view of a part of the plastic materialheader base plate and compliant member of FIG. 19, after tube endportions of the brazed matrix have been inserted through apertures inthe compliant member, with an expansion tool being used to expand thetube end portions and compress the compliant member to make to make aseal with the tube end portions;

FIG. 21 is a plan view inside of the plastic material header base plateshowing internal parts of the compliant member fitted to the header baseplate, taken along line XXI-XXI of FIG. 20 after withdrawal of theexpansion tool;

FIG. 22 is a is a cross-sectional view of a part of the joined matrix,plastic material header base plate and compliant member of FIG. 20,showing how a plastic material header cover is bonded to the header baseplate to complete the assembly of the heat exchanger in the thirdpreferred embodiment of the invention; and

FIG. 23 is a cross-sectional view of a part of a heat exchanger having avariant of the header of FIG. 22, in which the plastic material headercover is clipped to the header base plate to complete the assembly ofthe heat exchanger.

DETAILED DESCRIPTION

FIGS. 1 to 3 show the initial stages in the manufacture of a fusedassembly 7′ including a matrix 10 for a heat exchanger 100 such as thatas shown in FIG. 10 and in further embodiments of the invention, whichwill be described in more detail below. The embodiments all relate to amotor vehicle heat exchanger, although the principles of the inventionare applicable to other types of heat exchangers, both for cooling andheating purposes.

A plurality of elongate, longitudinally extending metallic tubes 2,which in this example are formed in aluminium, are first assembledspaced apart in a parallel orientation with metallic fins 4, also ofaluminium, in the spaces 6 between adjacent pairs of tubes. The tubes 2therefore bracket opposite top and bottom sides of each fin 4, except,optionally, for the end-most top and bottom fins which may be bonded onone side by a protective elongate, longitudinally extending component,which in this example is a solid metal strip 8, if it is desired toprovide greater mechanical protection at these locations. Although thedrawings show end strips 8 in the form of solid metallic bars, analternative is to omit these bars and the adjacent fins, in which casethe tubes 2 are not bracketed by any other component at the top andbottom locations.

FIG. 1 shows the tubes 2, fins 4 and protective end strips 8 prior tobrazing of the components. The components are therefore initially looseand not connected. To hold the components together during subsequentprocessing, a frame or one or more straps are temporarily placed aroundthe components to form a held assembly 7. This is shown, in a schematicform only, by the bracket-shaped lines 12 in FIG. 2.

With the components 2, 4, 8 thus held together, these are subjected to aheating and fusing process, which in this example is a controlledatmosphere brazing (CAB) process 11, as shown in FIG. 3. This process isa conventional process, known to those skilled in the art, for exampleused to manufacture all-metal heat exchangers including headers orheader base plates connected at the ends of the tubes, and willtherefore not be described in detail.

It should be noted that, optionally, in some embodiments of theinvention, one end of the tubes 2 could be attached in a heating andfusing process to a metallic header, or one or both ends of the tubescould be attached in a heating and fusing process to a correspondingmetallic header base plate. These end components could be attached toone or both sides of the assembly 7 prior to the heating and fusingprocess, and then fused together with the matrix in the same process, orthese end components could be fused to a header or header base plate ina separate, later process. In each case, however, at least one tube endon at least one side will not be so joined and will remain separate andthen joined with a compliant mechanical joint, as will be described inmore detail below.

FIG. 3 therefore shows in outline both such headers or header baseplates in place on a moving conveyor belt, however, it is to beappreciated that FIG. 3 is schematic only and that the heating andfusing process is the same when there is just one or no header or headerbase plate present.

In the case where at least one header or header base plate is includedin the heating and fusing process, at least one of the elongate,longitudinally extending components, either the protective strips 8 ortube end portions 14, 14′ at the, or each tube end 13, 13′, will befused to the header to make a metal-to-metal joint. However, at leastone of the remaining tube ends at one or both headers will then not beso joined during the heating and fusing process, and these free tubeends will then in a subsequent stage of processing be connectedmechanically to the corresponding header in one of the ways to bedescribed in more detail below.

At the end of the CAB process 11, the tubes 2, fins 4 and optionally theprotective metal strips 8 are fused together with the metal of eachcomponent extending seamlessly to the metal of adjacent, touchingcomponents. Similarly, if one or both of the headers is included, thenat least some of the tube ends will be fused to corresponding aperturesin each header or header base plate, but at least one of the tube endswill remain free from a corresponding aperture. In the heating andfusing process, a metal-to-metal joint at a tube end can be preventedfrom forming by providing a sufficiently wide gap, for example a gap ofat least 1 mm with any adjacent surfaces of the header.

FIGS. 4 to 22 relate specifically to the case where there is no headeror base plate fused at any tube ends in the same process used to fusetogether the matrix 10, so that all the connections to tubes are to bemade mechanically. The metal strips 8 are, however, joined in a laterheating and fusing process to an external surface of a header base plate20 to provide mechanical rigidity at opposite top and bottom ends 17,17′ of the heat exchanger 100.

FIG. 4 therefore shows the fused assembly 7′ of FIG. 3 as comprisingjust the matrix 10. In this example, each tube 2 initially has freelyextending opposite longitudinal ends 13, 13′. Each of the tube endportions 14, 14′ is aligned in parallel with all the other tube endportions on each of the opposite left and right sides 16, 16′ of thematrix 10. The fins 4 extend across a central heat transfer portion 15of the tubes, which stops short of the tube end portions 14, 14′ so thatthe tube end portions extend freely to the sides of the heat transferportion and fins.

A header or header base plate is then mechanically coupled to the tubeend portions 14, 14′ on both sides 16, 16′ of the matrix 10. If just oneheader or header base plate is fully fused with the matrix in the CABprocess, then the process will involve mechanically joining one or moreof the tubes to the other header or header base plate on the other sideof the matrix.

In this example, two header base plates, one of which 20 is shown, areassembled together with a sheet-like compliant member 22 and moved in alongitudinal direction 24 towards the corresponding tube end portion 14.The complaint member has a flat base portion 21 and a plurality ofprojecting portions 36, each of which extends away from the base portion21. The compliant member 22 is elastic and therefore resilientlycompressible, being made for example from a synthetic rubber material.FIG. 5 shows the arrangement when assembled and FIG. 6 shows an insideend view of the header plate 20, the compliant member 22 and a tube endsurface 26 of the tube end 13.

In this example, the tubes 2 are formed of aluminium and have a singlelongitudinally extending channel 28. Although not illustrated, theskilled person will appreciate that such tubes may, however, be foldedand have one or more additional channels. A folded tube having twoside-by-side channels is often referred to as a ‘B-tube’ due to itscross-sectional shape perpendicular to a longitudinal axis 29 of thetube 10. Folded tubes offer increased strength compared to tubes havinga single channel, whilst allowing the use of thinner and lightermaterials in their construction. Single channel tubes are, however,better suited to having their ends expanded and sealed with a compliantmember, as will be explained in more detail below.

The tubes 2 and end strips 8 are typically formed from sheet metal, forexample aluminium. In the case of the tubes, two opposing edges of thesheet metal are brought together to form a seam along the length of thetube 2, and this seam is then brazed to seal the tube 2. The fins 4 arealso typically formed from sheet metal, for example aluminium, and inthis example each fin 4 is folded in a zigzag or triangular pattern.

As can be seen from a comparison of FIGS. 4 and 6, the heat transferportion 15 of each tube 2 is generally flattened such that it has afirst, wider or broader dimension 31 and a second, thinner or narrowerdimension 32. In particular, an outer wall 33 of the heat transferportion 15 of the tube comprises opposing, generally planar, broadportions or sides 34 and opposing, generally curved, narrow portions orsides 35 extending between the broad sides. The tube 2 is flattened sothat the seam (not illustrated) runs to extend across the narrowerdimension 32 of the tube 2. The heat transfer portion 15 is thereforeelongate in cross-sectional shape in a horizontal plane that extendstransversely to the length of each tube 2.

In the context of the present invention, the term “flat” or “flattened”is used in relation to an object having a broad thin shape, i.e. anobject having a relatively broad surface in relation to a thickness ordepth.

As shown in FIGS. 9 and 10, the plurality of tubes 2 extends between afirst header 41 and a second header 42 to convey a heat exchange fluidor coolant 40 between the headers. The tubes 2 are laterally spacedapart along the height of the heat exchanger 100, and the gaps 6 insideof which the fins are bonded are defined between opposing broad portions34 of the outer walls 33 of adjacent pairs of tubes 2.

Typically, in use, a heated coolant 40 flows through the tubes 2 and acooler fluid, for example air, flows through gaps or holes in the matrix10. Heat energy from the coolant is transferred to the walls 33 of thetubes 2 and then into the fins 4 and this heat energy is then radiatedfrom the outer surfaces of the tubes 2 and fins 4, aided by the flow ofthe cooler fluid or air. The flattened shape of the tubes 2 maximisestheir surface to volume ratio, increasing the efficiency of the heatexchanger 100, while at the same time providing strength and physicalprotection for the fins 4, which are substantially flush with the twoopposing shorter sides 35 of the heat transfer portion 15 of the tube 2on opposite front and rear faces of the matrix 10.

During operation of the heat exchanger 100, the matrix 10 is subject tothermal cycling (rise and fall of the temperature of the heat exchangercomponents) which is typically uneven and therefore leads to unevenstresses due to thermal expansion. Neighbouring tubes may expand todifferent degrees such that axial loads are imposed on the tubes 2 bytheir neighbours. This is not a problem within the matrix, which ismechanically robust, but can lead to failure when both headers arebrazed to a metallic header or header plate. Such header/tube jointsare, therefore, prone to failure because of the stress concentrationsthat occur along the header/tube joint, with failure most commonlyoccurring at the intersection of the curved, narrow portions 35 of thetube and the header base plate.

The current invention deals with this problem by providing, along atleast one of the headers, and most preferably both headers, one or moremechanical joints between the tubes and headers which permit some degreeof longitudinal movement for those tubes that are mechanically joined,while maintaining a good seal against egress of coolant.

In the first embodiment of FIGS. 4 to 10, the compliant member 22 hasone or more rims or lips 36 each one of which extends through the baseplate 20 in contact with an edge 37 of one of a plurality of apertures38 in the base plate 20. Each of the rims or lips 36 therefore providesa sealing portion of the compliant member 22 between each tube endportion 14, 14′ and base plate 20.

Although the drawings show the compliant member 22 as assembled with thebase plate 20 before the tube end portions 14, 14′ have been insertedinto the respective base plate apertures 38, and before the top andbottom end strips 8 have been welded at a seam 23 to an external surfaceof the base plate, it should be noted that the elasticity of thecompliant member 22 permits the projecting rims 36 of the compliantmember 22 to be inserted between the tube end portions 14, 14′ and thebase plate apertures 38 after the assembly of the matrix 10 to theheader base plate 20 and after fusing of the end strips 8 to the baseplate 20.

The compliant member 22 is then held between opposing surfaces of eachtube end portion 14, 14′ and the corresponding aperture 38 in the baseplate 20. Inside each rim 36 of the compliant member 22 is an aperture39 that matches the profile of the tube end portion 14, such that eachtube end portion 14 can slip inside a corresponding one of the apertures39 in the compliant member 22, as shown in FIG. 5.

As shown in FIGS. 7 and 8, an expansion tool 50 with a plurality oftapered noses 52 is then moved in a longitudinal direction 54 towardsthe corresponding tube end portions 14 and then pressed into openings 55at each end tube end 13. This causes the tube outer wall 33 to expand tomatch the shape of the tool nose 52. The broad portions 34 of the tubewall are expanded outwards. In this example, the opposing narrowportions 35 are also expanded outwards as the broad portions 34 moveapart. This creates an expanded tube end portion 44 having a taperedsection 56 in which the cross-section is progressively expanded and anendmost straight section 57 in which the cross-section is constant. Inthis way, the sealing portion 36 of the compliant member 22 iscompressed or pinched between the expanded tube end portion 44 and thebase plate aperture edge 37.

The constant cross-section is in contact with the compliant member 22,which is compressed in this process to make tight contact with theexpanded tube end portion 44. The length of the endmost straight section57 is sufficient such that this straight section remains in contact withthe aperture 39 of the compliant member rim 36 during relativelongitudinal movement of the expanded tube end portion 44 and header orheader base plate 20 owing to thermal cycling of the assembled heatexchanger 100.

When the tubes 2 expand or contract longitudinally, the compliant member22 permits some movement, preferably by flexing alone, although in someembodiments, a degree of slippage may be possible as long as the shapeof the compliant member is such that this cannot over time work itselffree. In this regard, although not illustrated, each aperture edge 37may be seated in a groove in an outer surface of the lip or rim of thecompliant member 22 which will then have groove walls that contact boththe outer and inner sides of the base plate 20 around the aperture edge37.

The assembly of each header 41, 42 is completed by fitting a headercover 58 to the header base plate 20. The header cover 58 may be metalor polymer, and may be joined to the base plate 20 along a seam 59 byconventional means, for example by gluing, crimping, or brazing. In thisexample, the compliant member 22 has a peripheral edge 61 that extendsaround the inside of a longitudinally projecting rim 62 of the headerplate. The compliant member edge 61 is compressed during this joining ofthe cover 58 by a peripheral lip 63 of the cover in order to make theseal. This also provides the benefit of securing the compliant member 22in place so that this does not slip in a lateral direction.

In the case where some, but not all, of the tube ends 13 are to be fusedto the header or the header base plate 20 in the heating and fusingprocess 11 or afterwards, those tube ends which are to be fused areplaced substantially in contact with the edges of an aperture (i.e. incontact with or separated by preferably no more than about 0.1 mm). Theaperture edge then has smaller dimensions wherein the tube wall 33 atthe tube end surface 26 overlaps the aperture edge. Each of theapertures is therefore correspondingly reduced in size from thoseillustrated, to match the dimensions of the opening 55 at the tube end.In the case of an aperture where no such fusing of metal is to occur,the base plate apertures 37 are sized as shown in the drawings so thatthe tube ends 13 at these apertures remain free. Such tube ends may,optionally, be longer than those to be fused, so that the free tube ends13 protrude through each base plate aperture by the amount shown in FIG.7, whilst the fused tube ends can be terminated at a shorter length,similar to that of the protective strip 8, where these are joined to themetal of the header base plate. Each free tube end is then positionedwith a clear gap between the tube end and the corresponding aperture.The compliant member 22 is then inserted over the tube ends 13 and intothis gap, after which the tube ends are expanded by a tool as describedabove to crimp the compliant member.

Although the above description relates to an assembly with a singlecomponent providing the compliant member for sealing each tube endportion, there may be multiple, physically separate compliant members,each one of which extends around the periphery of each base plateaperture. This embodiment, in which some, but not all, of the tube ends13 are to be fused to the header or the header base plate, is suited toseparate compliant members, one for each expanded tube end portion 44 tobe sealed.

Therefore, the invention extends to the case where there is acombination of metal fused joints and mechanical joints along one orboth of the headers. Such an arrangement may be desirable becausemetal-to-metal fused joints will, in general, be less expensive toachieve in a manufacturing process than mechanical joints. In practice,it has been found that not all metal-to-metal joints between tube endsand the respective headers or header base plates are equally likely tofail owing to thermal stresses.

As an example of this, in FIG. 10, one of the headers 41 has an internaldividing wall 65 which separates the header into an inlet side and anoutlet side. Relatively hotter coolant 40 will therefore flow out of aninlet port 43, into the inlet side of the header and into a first set oftubes and relatively cooler coolant will flow in a directly adjacentsecond set of tubes towards the outlet side of the header and an outletport 45. In this arrangement, the two joints most likely to fail arethose connected to the first header 41 closest on either side of theinternal dividing wall 65, because this is where there is the greatestdifference in temperature between adjacent tubes. Therefore, for thisexample the maximum benefit from the invention, for the leastmanufacturing cost, will be to provide mechanical joints just to thosetwo tubes connected on either side of the dividing wall 65 that wouldotherwise be subjected to the greatest stress, leaving other tubes witha metal-to-metal fused joint.

The particular choice of which tubes should have mechanical joints will,therefore, depend on the particular design and use of the heat exchanger100.

When there are no ends strips 8 joined to the headers or base plates,then there is a particular advantage in providing at least the twooutermost tubes at opposite top and bottom ends of the array of tubeswith a metal-to-metal fused joint to the headers or base plates, as thiswill provide a solid connection and will therefore prevent anyintervening mechanical joints from ever working apart.

FIGS. 10 to 17 show a second embodiment of the invention, in whichfeatures similar to or the same as those of the first embodimentdescribed above, are indicated using reference numerals incremented by100.

The second embodiment differs from the first in two main respects.First, the compliant member 122 is assembled to the base plate 120 fromthe opposite side, i.e. from the outside of the base plate 120 facingthe matrix 110. As in the first embodiment, the compliant member 122provides apertures 139 that match the profile of the tube end portion114, such that each tube end portion 114 can slip inside a correspondingone of the apertures 139 in the compliant member 122. The compliantmember 122 therefore needs to be assembled to the base plate 120 beforethe tube end portions 114 are inserted into corresponding apertures 138in the base plate 120, and before the protective strip 108 is fused tothe outside of the header base plate 120.

The second main difference is that each aperture 138 provided in thebase plate 120 is bounded by a wall 70 that provides the edge 137 toeach aperture 138 and which extends parallel with the tube axis 129 toform U-shaped portions in between each aperture 138. The compliantmember 122 has a base portion 121 in contact with the external surfaceof the header plate and a plurality of projecting portions 136 thatextend away from the base portion 121 parallel with the tube axis 129with a greater length relative to those projecting portions 36 of thefirst embodiment. The projecting portions 136 provide the sealingportions of the compliant member 122.

The effect of these changes is to increase the surface contact area ofthe compliant member sealing portion 136 against the respective tube endportion 114 and the aperture edge 137. This is useful as in thisconfiguration seating of the compliant member 122 will need to resistoutward forces from the coolant, which will generally be circulating ina pressurized circulation loop.

In this embodiment, the base plate 120 is of metal so that the apertureedges 137 can be deformed by the tool 150. As shown in FIGS. 14, 16 and18, the invention further improves the seating of the compliant member122 by crimping both the tube end portions 114 and the walls 70 in orderto compress the sealing portions of the compliant member 122 fromopposite sides.

An expansion tool 150 with two different types of tapered noses, onetype 152 for the tube end openings 155 and the other type 152′ for thebase plate aperture walls 70, is then moved in a longitudinal direction154 towards the corresponding tube end portions 114 and then pressedinto openings 155 at each end tube end 113. This causes the tube outerwall 133 to expand to match the shape of the corresponding tool nosetype 152. At the same time, the other tool nose type 152′ causes theaperture walls 70 to deflect towards the adjacent tube end portions 114.Although not shown in the drawing, this happens around the fullperiphery of each base plate aperture 138. In this way, the syntheticrubber sealing portion 136 of the compliant member 122 is compressed orpinched between the expanded tube end portion 114 and the base plateaperture edge 137.

The broad portions 134 of the tube wall are expanded outwards. In thisexample, the opposing narrow portions 135 are also expanded outwards asthe broad portions move apart. This creates an expanded tube end portion114 having a tapered section 156 extending all the way to the tube end113 in which the cross-section is expanded. When the tubes 102 expand orcontract longitudinally, the compliant member 122 permits some movementby flexing alone.

Although not illustrated, the assembly of each header is completed byfitting a header cover to the header base plate in the same way as inthe first embodiment.

The invention is also applicable to headers and header base plates madefrom a polymer material, however, in this case there will, of course, beno metal-to-metal fused joints. A mechanical joint with a polymer headermay be made in the same manner as described above, however, polymermaterials provide other ways in which to compressibly seat the tube endportion in a compliant edge seal.

FIGS. 18 to 22 shows a third embodiment of the invention and FIG. 23shows a variant of this embodiment, in which features similar to or thesame as those of the first embodiment described above, are indicatedusing reference numerals incremented by 200.

The third embodiment differs from the first embodiment mainly in thatthe header has a polymer material base plate 220 and a polymer materialcover 258. As in the first embodiment, the synthetic rubber compliantmember 222 is seated inside the header plate, and has a base portion 221in contact with the internal surface of the header plate and a pluralityof projecting portions 236 that extend away from the base portionparallel with the tube axis 229.

As the base plate 220 is formed in a known injection moulding process,the base plate 220 can easily be provided with varying wall thicknesses,and so the base plate 220 has a portion 72 with a trapezoidalcross-section or arrow head cross-section in between each base plateaperture 238, and which extends around the ends of each aperture andaround the two outermost apertures as two angled wall surfaces, one ofwhich 73 is parallel with the tube axis 229 and the other of which 74 isangled away from the aperture 238 and the tube axis 229. The compliantmember 222 has the inverse shape so as to make full contact with thesetwo angled wall surfaces 73, 74. The projecting portions 236 of thecompliant member 222 therefore have a greater length relative to theprojecting portions 36 of the first embodiment in order to engage fullywith the two angled wall surfaces 73, 74.

As in the first embodiment, the compliant member 222 provides apertures239 that match the profile of the tube end portion 214, such that eachtube end portion 214 can slip inside a corresponding one of theapertures 239 in the compliant member 222. After insertion of the tubeend portions 214 into the apertures 239, an expansion tool 250 having aplurality of tapered noses 252 is inserted into tube openings 255 toexpand the tube end portions. This causes the tube outer wall 233 toexpand to match the shape of tool noses 252 around the full periphery ofeach base plate aperture 238. In this way, the sealing portion 236 ofthe compliant member 222 is compressed or pinched between the expandedtube end portion 244 and the two angled wall surfaces 73, 74 that definethe base plate aperture edge 237.

The broad portions 234 of the tube wall are expanded outwards. In thisexample, the opposing narrow portions 235 are also expanded outwards asthe broad portions 234 move apart. This creates an expanded tube endportion 244 having a tapered section 256 extending all the way to thetube end 213 in which the cross-section is expanded. When the tubes 202expand or contract longitudinally, the compliant member 222 permits somemovement by flexing alone.

The assembly of each header 241 is completed by fitting a header cover258 to the header base plate 220. FIGS. 22 and 23 show two ways in whichthis can be done.

In FIG. 22, the cover 258 has a peripheral lip 263 with a groove 76 intowhich a longitudinally projecting rim 262 of the base plate fits. Thepolymer material cover may then be joined to the polymer material baseplate by vibration welding or by gluing.

In FIG. 23, the compliant member 222′ has the same form as that of FIG.22, but is extended laterally to reach the base plate rim 262′. The baseplate rim 262′ has around its outer periphery a series of laterallyoutwardly projecting detents one of which 77 is shown in cross-section.Each detent 77 snaps into engagement with a ledge 78 at the end of anopen slot 79 in the cover 258′. In this process, a peripheral lip 263′of the cover 258′ inserts inside the base plate rim 262′. The compliantmember 222′ has a peripheral edge 261 that extends around the inside ofthe longitudinally projecting rim 262′ of the header base plate. Thecompliant member edge 261 is compressed during this joining of the cover258′ by the peripheral lip 263′ of the cover in order to make the seal.This also provides the benefit of securing the compliant member in placeso that this does not slip in a lateral direction.

When the header is a polymer header, as in FIGS. 22 and 23, there willbe no join between the all-metal matrix and the polymer header formedusing a heating and fusing process. Therefore, as shown in FIGS. 22 and23, when there is a strip 208 extending across the matrix between theheads, this will not be joined to the headers.

The compliant members in the various embodiments described above aremost preferably made from ethylene propylene diene rubber (EPDM).Alternatively, a silicone rubber material may be used.

The skilled person will appreciate that heat exchangers can, in general,be operated in any orientation. Therefore, references in thisspecification to top and bottom, left and right, up and down, horizontaland vertical are to be read accordingly, but are not to be taken asbeing exact orientations and thereby limiting the scope of theinvention.

The present invention, therefore, provides a heat exchanger that hasimproved durability against thermal cycling while maintaining good heattransfer efficiency.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes may be made without departingfrom the scope of the disclosure, which is further described in thefollowing appended claims.

The invention claimed is:
 1. A heat exchanger comprising: an all-metalbonded matrix including a plurality of substantially parallel metallictubes and a plurality of metallic fins, the tubes having a heat transferportion, the heat transfer portion having an elongate cross-sectionalshape and comprising two opposing longer sides, and two opposing shortersides, and the fins disposed between the opposing longer sides of theheat transfer portion of adjacent tubes; and a first header and a secondheader, each of the tubes having at opposite ends thereof a first endportion and a second end portion, the first end portion and the secondend portion joined respectively to the first header and the secondheader, the matrix thereby configured to transfer heat between anexternal medium and a coolant conveyed between the first header and thesecond header by the tubes; wherein at least one of the tubes ismechanically joined at the first end portion to the first header by atleast one compliant member, the compliant member extending around thefirst end portion to provide a seal with the first end portion for thecoolant held within the heat exchanger and permitting relative movementbetween the at least one of the tubes mechanically joined and the firstheader due to thermal expansion and contraction of the matrix; whereinthe matrix further comprises at least one strip arranged substantiallyparallel with the tubes, the at least one strip disposed at one end ofthe matrix and in contact with an external surface of the first headerand an external surface of the second header to provide a mechanicalrigidity of a connection formed between the matrix and each of the firstheader and the second header, wherein the first header has an internaldividing wall which separates the first header into an inlet side and anoutlet side, wherein the tubes include a first tube closest to thedividing wall at the inlet side, a second tube closest to the dividingwall at the outlet side, and other tubes, wherein the first tube and thesecond tube are mechanically joined to the first header, and wherein theother tubes are metal bonded to the first header.
 2. The heat exchangeras claimed in claim 1, wherein at least one of the tubes is joined atboth the first end portion and the second end portion thereof tocorresponding ones of the first header and the second header by anall-metal bond formed between the first end portion and the second endportion and the first header and the second header.
 3. The heatexchanger as claimed in claim 2, wherein there is a plurality ofall-metal bonded tubes, and the at least one of the tubes mechanicallyjoined is disposed in between the all-metal bonded tubes.
 4. The heatexchanger as claimed in claim 1, wherein: the first header has a firstbase plate with a plurality of apertures; each of the end portions isreceived within a corresponding one of the apertures of the first baseplate; and a sealing portion of the compliant member is interposedbetween an edge forming the aperture in the first base plate and thefirst end portion of the at least one of the tubes mechanically joined,the first end portion thereby mechanically joined to the first header.5. The heat exchanger as claimed in claim 4, wherein the first endportion of the at least one of the tubes mechanically joined has anexpanded portion, the sealing portion of the compliant member compressedaround the aperture by the expanded portion of the at least one of thetubes mechanically joined.
 6. The heat exchanger as claimed in claim 5,wherein the expanded end portion has an enlarged cross-sectional shaperelative to the heat transfer portion, the enlarged cross-sectionalshape compressing the sealing portion of the compliant member betweenthe first end portion and the aperture of the first base plate.
 7. Theheat exchanger as claimed in claim 5, wherein the expanded end portionhas an elongate cross-sectional shape, and comprises two opposing,longer sides, and two opposing shorter sides.
 8. The heat exchanger asclaimed in claim 7, wherein an outwardly tapered section of the tubeextends from the heat transfer portion towards the expanded end portionwherein the distance between the two opposing longer sides is increasedand the distance between the two opposing shorter sides is increased. 9.The heat exchanger as claimed in claim 7, wherein the first end portionof the at least one of the tubes mechanically joined has an opening forconveying the coolant, the two opposing longer sides of the expanded endportion splayed outwards proximate the opening and the two opposingshorter sides of the expanded end portion splayed outwards proximate theopening.
 10. The heat exchanger as claimed in claim 5, wherein theexpanded end portion has a section with a substantially constantcross-sectional shape in contact with the sealing portion of thecompliant member, whereby the sealing portion is neither compressed norexpanded, owing to relative movement of the first end portion of the atleast one of the tubes mechanically joined and the first header due tothermal expansion and contraction of the matrix.
 11. The heat exchangeras claimed in claim 4, wherein the compliant member has a base portionand at least one projecting portion, the base portion seated on asurface of the first base plate and the at least one projecting portionextending through a corresponding one of the apertures in the first baseplate, whereby the sealing portion of the compliant member is interposedbetween the first base plate and the first end portion of the at leastone of the tubes mechanically joined.
 12. The heat exchanger as claimedin claim 11, wherein the base portion of the compliant member is a sheetwith a plurality of apertures formed therein, each of the apertures inthe sheet having a raised rim that forms the projecting portion, theraised rim of the apertures extending through a corresponding one of theapertures in the first base plate, whereby the raised rim of each of theapertures is interposed between the first base plate and the first endportion of the at least one of the tubes mechanically joined to providethe sealing portion.
 13. The heat exchanger as claimed in claim 12,wherein the base portion of the compliant member is seated on anexternal surface of the first base plate facing substantially towardsthe matrix.
 14. The heat exchanger as claimed in claim 12, wherein thebase portion of the compliant member is seated on an internal surface ofthe first base plate facing substantially away from the matrix.
 15. Aheat exchanger as claimed in claim 14, wherein the first base plate hasa periphery and the first header has a header cover joined to theperiphery of the first base plate, the first header cover and the sheetextending to the periphery of the first base plate and providing a sealaround the periphery of the first base plate between the first baseplate and the first header cover.
 16. A method of manufacturing a heatexchanger, the heat exchanger comprising an all-metal bonded matrix, themethod comprising the steps of: forming a first header, the first headerhaving a first set of apertures; forming a second header, the secondheader having a second set of apertures; forming a plurality of elongatemetallic tubes, each of the tubes having a first end portion and asecond end portion and an opening at both of the first end portion andthe second end portion for conveying a coolant through the tubes fromthe first header to the second header, and each of the tubes havingbetween the first end portion and the second end portion a heat transferportion for transferring heat with an external medium, the heat transferportion having an elongate cross-sectional shape, and comprising twoopposing longer sides, and two opposing shorter sides; forming aplurality of metallic fins; orienting the tubes and the fins wherein thetubes are substantially parallel with one another and with the finsextending between the opposed longer sides of adjacent pairs of thetubes; holding temporarily the oriented tubes and fins with at least onestrap; using a heating and fusing process to join together the tubes andthe fins to form the all-metal bonded matrix, the matrix having a firstface and a second face wherein an external medium may flow through thematrix from the first face to the second face to effect a transfer ofheat between the coolant conveyed by the tubes and the external medium;removing the at least one strap after the heating and fusing process;aligning the first end portions with the first set of apertures andaligning the second end portions with the second set of apertures andjoining each of the first end portions and the second end portions tothe corresponding aligned set of apertures; and receiving the first endportion of at least one of the tubes within a corresponding aperture ofthe first set of apertures and using a compliant member to join the atleast one of the tubes to the first header in a mechanical joint betweenthe first end portion of the first header and the corresponding aperturewithin which the first end portion is received, the compliant memberproviding a seal around the first end portion for the coolant andpermitting relative movement along the length of the at least one of thetubes mechanically joined between the joined first end portion and thefirst header due to thermal expansion and contraction of the matrix,wherein the first header has an internal dividing wall which separatesthe first header into an inlet side and an outlet side, wherein thetubes include a first tube closest to the dividing wall at the inletside, a second tube closest to the dividing wall at the outlet side, andother tubes, wherein the first tube and the second tube are mechanicallyjoined to the first header, and wherein the other tubes are metal bondedto the first header.
 17. The method as claimed in claim 16, furthercomprising the steps of: forming a first base plate, the first set ofapertures provided in the first base plate; forming a second base plate,the second set of apertures provided in the second base plate; forming afirst header cover and assembling the first header cover to the firstbase plate to form the first header; and forming a second header coverand assembling the second header cover to the second base plate to formthe second header.
 18. The method as claimed in claim 17, wherein thefirst base plate has a periphery, the compliant member extending to theperiphery inside the first header, the method further comprising thestep of joining the first header cover to the first base plate at theperiphery with the compliant member providing a seal between the firstheader cover and the first base plate at the periphery.
 19. The methodas claimed in claim 17, wherein the second base plate is metallic andthe method further comprises the step of joining each of the tubes atthe second end portions thereof to the second header by an all-metalbond in a heating and fusing process between the second end portions andthe second header.